Rebecca Sproule NewGenCo Pty Ltd, Geodiscovery Group, Perth, Western Australia

C. Michael LesherDepartment of Earth Sciences, Laurentian University, Sudbury, Ontario

PGE potential of Ultramafic-Mafic Intrusions in Ontario:

Vectors to PGE mineralization and where next…..

PGE potential of Ultramafic-Mafic Intrusions in Ontario:

Vectors to PGE mineralization and where next…..

Project SponsorsProject SponsorsOperation Treasure Hunt Project (Ontario Geological Survey 2001-2002)

Christine Vaillancourt & Carole-Anne MacDonaldNSERC CAMIRO

IntroductionIntroductionAims were to identify key criteria for PGE prospectivityPetrogenesis and metallogenesis of 109 mafic-ultramafic intrusions in Ontario (Canada) was determined

n = 4830Range includes:

Archean to Palaeoproterozoic intrusionsKomatiitic, tholeiitic, calc-alkalic, alkalic and sanukitoid magmatic affinitiesPGE mineralized economic to PGE-subeconomic to non-mineralised

Importantly, WE ANALYSED BARREN INTRUSIONS TO UNDERSTAND THE COMPLETE SYSTEM!!

Mineralization TypesMineralization Types

Trout Baytectonically mobilizedV

Lac des Iles hydrothermally-metamorphically deposited or mobilized

IV

Moshkinabi, Centre Hill, Ghost Range, Seagull, Coldwell

stratiform reef-style III

Roaring Riverstratabound internal disseminated

II

Coldwell, Kawene, Shakespeare, TibLake, Seagull

contact/marginalI

ExamplesDistributionType

Type 1: Contact marginal: Net-textured ore, Alexo Mine, Dundonald Township

Type 2: Internal stratibound disseminated: Ccp-Po blebs in gabbro, Entwine Lake (Jason Arnold)

Type 3: Reef Type: Layered gabbro, Moshkinabi (Christine Vaillancourt)

Type 4: Hydrothermally remobilized Roby Zone –varitextured

Type 4: Hydrothermally remobilized Roby Zone Type 4: Hydrothermally remobilized Roby Zone ––varitextured varitextured

Type 5: Mineralized SUIF, Trout Bay area, Red Lake region (Christine Vaillancourt)

Type 5: Ni-Co-PPGE arsenide mineralization in recrystallized Amph-Chl-Tc rock, Peterson property, Red Lake region (Christine Vaillancourt)

Ni-Co arsenide Pyrrhotite

2 cm

PetrogenesisPetrogenesis

0.1

1

10

0.01 0.1 1 10

[Nb/Th]MN

[La/

Sm] M

N

Coldwell Complex Nipissing GabbroQuetico McVicar LakeJuly Falls Trout BayLac des Iles-MBI Tib LakeRoaring River Mulcahy Moshkinabi White LakeCentre Hill Complex Ghost RangeKamiskotia Mann intrusionOtto Caribou LakeSeagull intrusion ShakespeareMORB OIBE-MORB Proterozoic Pelitic Rock

Continental crust N-MORB mixed Continental crust E-MORB mixed

EnrichedMantle

Upper Continental Crust

DepletedMantle

DifferentContaminant?

La mobility?

Crustal contamination versus Enriched sourceCrustal contamination versus Enriched source

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10

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10000

0 10 20 30 40 50 60 70 8090 100

Σ[R

EE] M

N

LDI-MBI

LDI-NUMI

LDI_CL

Nipissing Gabbro

Quetico

McVicar Lake

July Falls

Trout Bay

Tib Lake

Roaring River

Mulcahy

Moshkinabi

Coldwell Complex

White Lake

Centre Hill Complex

Ghost Range

Kamiskotia

Mann intrusion

Otto

Caribou Lake

Seagull intrusion

Shakespeare Cumulate rock with 20% intercumulus material (depleted mantle source region)

Cumulate rock with 20% intercumulus material (depleted mantle source region + 10% crustal contamination)

Enriched source

Unenriched source (normal depleted mantle)

Mg#

Decreasing intercumulus liquid

Crustal contamination versus Enriched sourceCrustal contamination versus Enriched source

Note low S/Se ratios of LDI-MBI and Trout Bay

1

10

100

1000

10000

100000

1000000

0 10 20 30 40 50 60 70 80 90 100

Mg#

log(

S/Se

)

Nipissing Gabbro QueticoMcVicar Lake July FallsTrout Bay Tib LakeRoaring River Mulcahy Moshkinabi Coldwell ComplexWhite Lake Centre Hill ComplexGhost Range KamiskotiaMann intrusion OttoCaribou Lake Seagull intrusionShakespeare LDI-MBILDI-CL LDI-NUMI

Magmatic

Crustal

S-loss

Crustal contaminationCrustal contamination

Continental Crustal Contamination

Ghost RangeWhite Lake

Mulcahy

MannTrout Bay

Centre HillNormal depleted

McVicar Lake Kamiskotia

Caribou Lake

MoshkinabiMulcahy

Strongly Depleted(refractory)

ShakespeareColdwell ColdwellLac des Iles - MBI

Lac des Iles - NUMIKawene

Roaring RiverJuly Falls

Otto

Strongly Depleted(refractory), then metasomatically enriched

SeagullSeagull

Enriched

Tib LakeNormal depleted, then metasomatically enriched

UniformLocalNone to MinorMantle Source

Magma TypeMagma TypePGE mineralization is hosted by intrusions derived from a variety of magma types

Most magmas form PGE mineralizationTholeiitic intrusions most commonly host PGE mineralizationAlkaline intrusions with large abundances of mafic-ultramafic rocks are a less common host of PGE mineralization

Source CompositionSource Composition

The most significant PGE reserves andresources (e.g., Coldwell Complex, Lac des Iles, Seagull, Shakespeare) are from intrusions from enriched or metasomatized mantle sources (e.g., sub-arc mantle)PGE mineralization is also associated with intrusions from normal depleted mantle (e.g., Moshkinabi and Mann intrusions)

Such PGE mineralization is typically of lower tonnage and grade

Degree of Partial MeltingDegree of Partial Melting

The degree of prior melt extraction is not important

mineralized intrusions are derived from sources that have experienced variable degrees of prior partial melting

Magma Diversification Processes

Magma Diversification Processes

Mineralized intrusions are either uncontaminated or only locally contaminated by upper crust

Where contaminated, may have aided in triggered sulfide saturationWhere uncontaminated, sulfide saturation was likely induced by fractionation crystallizationIn some cases (e.g., Lac des Iles), PGE may have also been concentrated into late-stage volatile-rich phases

Magma Diversification Processes

Magma Diversification Processes

Intrusions that are uniformly contaminated rarely host significant tenors/tonnages of PGE mineralization

can host significant amounts of Ni-Cu-PGE mineralization

e.g., the Shakespeare intrusion

MetallogenesisMetallogenesis

0.0001

0.001

0.01

0.1

1

10

100

1000

10000

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1000000

0 10 20 30 40 50 60 70 80 90 100

[Pd/

Zr] M

N

Nipissing GabbroQueticoMcVicar LakeJuly FallsTrout BayTib LakeRoaring RiverMulcahy MoshkinabiColdwell ComplexWhite LakeCentre Hill ComplexGhost RangeKamiskotiaMann intrusionOttoCaribou LakeSeagull intrusionShakespeare FCAFCLDI-MBILDI-CLMBI-NUMI

Enrichment of Pd related to accumulation of PGE-rich sulfides

Depletion of Pd related to loss of PGE-enriched sulfides

Mg#

Identification of PGE rich magmasIdentification of PGE rich magmas

McVicar Lake, Otto Stock, White Lake, July Falls, Caribou Lake

Uniformly depleted

MulcahyDepleted in PGE, but not Ni or Cu

Shakespeare, Nipissing GabbroDepleted in PGE, Ni, and Cu above mineralized zone

Kawene, Ghost Range, Kamiskotia, Lac des Iles-CL

PGE follow FC trend, and lowest Mg# rocks are depleted

Moshkinabi, Centre Hill,Seagull/Seagull, Nipissing Gabbro

PGE follow FC trend, high PGE rocks have accumulated sulfide, and lowest Mg# rocks are depleted

Coldwell/Coldwell, Roaring River, Mann/Mann, Lac des Iles-NUMI

Elevated Pt, Pd, but lowest Mg# rocks are depleted

Lac des Iles-MBI, Trout Bay, Tib Lake

Elevated Pt, Pd

IntrusionTrend

Sulfide-Saturation History and Mineralization Type

Sulfide-Saturation History and Mineralization Type

Type I contact-type mineralization is associated with rocks containing elevated to normal abundances of PGEs

In most cases, the rocks overlying the mineralized zones are depleted in PGEs

Type II internal disseminated mineralization is associated with rocks containing high abundances of PGEs

However, other, typically more fractionated, portions of the intrusions can be depleted in PGEs

Type III reef type mineralization is associated with rocks containing normal PGE abundances, but enrichment in samples with accumulated PGEType IV hydrothermally-deposited or hydrothermally-mobilized mineralization is associated with PGE-enriched magmas (in Ontario)

Sulfide-Saturation History and Mineralization Type

Sulfide-Saturation History and Mineralization Type

Some intrusions are depleted in PGE, but not Ni or Cu, suggesting that some PGE-enriched sulfides were lost during ascent and/or emplacement

Such intrusions still have potential to host Ni-Cu deposits

Some intrusions are uniformly depleted in PGE and have little potential for PGE mineralization

Sulfide-Saturation History and Mineralization Type

Sulfide-Saturation History and Mineralization Type

Sulfide-Saturation History and Mineralization Type

Sulfide-Saturation History and Mineralization Type

Mineralized intrusions with the mostsignificant PGE mineralization (highest grade and largest tonnage) have high background PGE abundances for theirMg# or MgO content

SummarySummaryMineralized intrusions with the most significant PGE mineralization (highest grade and largest tonnage) have the high background PGE abundances for their Mg# or MgO contentIntrusions derived from enriched sources should be preferentially explored for PGE mineralization

Such rocks have high abundances of MILE (Ti, Zr, MREE-HREE) and very high abundances of all HILE (e.g., Cs, Rb, U, Th, Nb, Ta, LREE)

Intrusions derived from normal depleted sources are still good targets for PGE mineralization, but are not as favourable

SummarySummaryIn all cases where significant PGE mineralization is present, a specific process has “triggered” PGE segregation: crustal contamination, magma mixing, and/or fractionation crystallizationUniformly contaminated intrusions have low PGE potential, but such intrusions may host Ni-Cu mineralizationThe degree of prior melt extraction is not a significant factor for PGE prospectivity

So what’s the important message out of this for exploration and future work research work…..

So what’s the important message out of this for exploration and future work research work…..

In Ontario:The best intrusions have high background PGE abundancesThe intrusions from the best areas have enriched metasomatised mantle

Prospective zones with enriched mantle can be mapped out

Where next….Fennoscandia – do the same relationships apply?